Electrical power distribution systems manage the allocation of power from energy sources to electrical loads that consume distributed electrical power. In aircraft, gas turbine engines for propulsion of the aircraft typically provide mechanical energy that ultimately powers a number of different accessories such as generators, starter/generators, permanent magnet generators (PMG), fuel pumps, and hydraulic pumps, e.g., equipment for functions needed on an aircraft other than propulsion. For example, contemporary aircraft need electrical power for electrical loads related to avionics, motors, and other electric equipment.
Over time, aircraft electrical power source voltages have increased. Aircraft with 14- and 28-volt direct current (VDC) electrical power systems have given way to aircraft with electrical power systems operating at 115 volts alternating current (VAC) and 230 VAC. Presently, aircraft can include one or more electrical power sources that operate at voltages including plus/minus 270 VDC. For example, a current wide-body twin-engine commercial jetliner uses an electrical system that is a hybrid voltage system that includes sub-systems operating at voltages of 230 VAC, 115 VAC, 28 VDC along with a bipolar, high voltage, direct current subsystem that includes plus and minus 270 VDC sources.
The voltages in the high-voltage DC electrical systems reach levels comparable to domestic AC systems and need to include fault mitigation features to detect and react to abnormal electrical current flow that can occur in the system. In domestic AC systems fault protection devices typically include a circuit breaker that can trip to an off position, typically by way of an electromechanical switch that can actuate in approximately 50 milliseconds (ms) to de-energize the feed line in the event of a fault condition. An electromechanical switch passing current from a high-voltage DC source to an electrical load draws an arc on opening the switch when the electron flow across the opening switch contacts ionizes the air molecules across the gap between the contacts to form a gas plasma. The plasma is of low resistance and is able to sustain power flow. The plasma is hot and capable of eroding the metal surfaces of the switch contacts. Electric current arcing causes degradation of the contacts and therefore the electromechanical switch and also electromagnetic interference (EMI) that can require the use of arc suppression methods.